In testing semiconductor devices, it is important to control and maintain an accurate stable thermal environment. Semiconductor devices generally undergo a variety of tests to insure proper operation. During testing, for example, the power level of the device under test (DUT) may vary, causing significant temperature changes of the device. In dealing with this problem there are various conventional techniques to respond to the temperature variations of the device.
Feedback methods are commonly used to sense the temperature variations of the device using a temperature sensing device mounted on the die, case, or heat sink. Some of the problems with these methods are long delays in the feedback and temperature control response time.
Another approach is power following feedback, measuring real time power usage of the device. The real time power measurement of the device is used to determine the real time temperature of the device. One deficiency of power following feedback is that it only follows the power variations not considering other predictive parameters such as frequency, doping levels, simulation results, outside temperature, etc. Without the additional parameters it is impossible for a power following approach to adaptively respond to the full test needs of the DUT. Another deficiency is that it does not control the slow response time of automatic thermal control (ATC) system, thus resulting in temperature over shoot and/or under shoot of the DUT. The power following technique may result in excessive amounts of heating and cooling of the DUT in response to power changes, which is far from optimal.